mtd: remove R/O checking duplication

Many drivers check whether the partition is R/O and return -EROFS if yes.
Let's stop having duplicated checks and move them to the API functions
instead.

And again a bit of noise - deleted few too sparse newlines, sorry.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/chips/map_ram.c

@@ -122,14 +122,10 @@ static int mapram_erase (struct mtd_info *mtd, struct erase_info *instr)
 	unsigned long i;
 
 	allff = map_word_ff(map);
-
 	for (i=0; i<instr->len; i += map_bankwidth(map))
 		map_write(map, allff, instr->addr + i);
-
 	instr->state = MTD_ERASE_DONE;
-
 	mtd_erase_callback(instr);
-
 	return 0;
 }